This invention relates generally to the field of frequency standards, and in particular, it concerns a miniaturized atomic frequency standard.
Modern military, aerospace and communications systems often require extremely stable and accurate timing devices, with the overall size, weight and ruggedness of the device being important considerations. Atomic frequency standards have for some time been used in such applications, for example the atomic clock disclosed in U.S. Pat. No. 4,943,955 issued to Rabian et al. However, atomic frequency standards have the disadvantages of bulky component construction and high cost. U.S. Pat. No. 4,494,085 issued to Goldberg describes one technique for reducing the size of an atomic clock by reducing the size of its microwave cavity. Goldberg decreases the overall size of the cavity by placing both a filter cell and an absorption cell in the cavity. An alternative to obtaining a miniature atomic frequency standard is the harmonic optical oscillator described in U.S. Pat. No. 4,961,119 issued to Irish. That patent teaches a solid state device integrated on a microchip, with its inherent size and weight advantages, however, that device is expected to maintain an accuracy of only about 1/2 second per year, far less than the capability of an atomic frequency standard.
L. L. Lewis is attempting to reduce the size of a cesium beam atomic frequency device by using shorter beam lengths and a single microwave interaction region, as described in his article entitled Miniature Optically Pumped Cesium Standards, published by the IEEE in the Transactions of the Forty-Fifth Annual Symposium on Frequency Control, 1991. The overall volume goal of this work is one liter--about the size of existing rubidium cell devices.
Therefore, a need still exists for a highly accurate frequency standard with a reduced size compared to existing devices.